VEGF R1 (Flt-1), VEGF R2 (KDR/Flk-1), and VEGF R3 (Flt-4) belong to the class III subfamily of receptor tyrosine kinases (RTKs). All three receptors contain seven immunoglobulin-like repeats in their extracellular domain and kinase insert domains in their intracellular region. They are best known for regulating VEGF family-mediated vasculogenesis, angiogenesis, and lymphangiogenesis. They are also mediators of neurotrophic activity and regulators of hematopoietic development. Human VEGF R2 is thought to be the primary inducer of VEGF-mediated blood vessel growth, while VEGF R3 plays a significant role in VEGF-C and VEGF-D-mediated lymphangiogenesis.